Proteins such as enzymes or antibodies as well as fragments thereof are unstable and susceptible to loss of activity and/or to formation of soluble or insoluble aggregates in aqueous solutions and when stored at low temperatures (below 0.degree. C.) and in particular in repeated freezing and thawing processes and these aggregates become apparent by forming particles and thus as turbidities. However, such aggregate and/or particle formation cannot be tolerated or at least only in traces for pharmaceutical compositions of proteins. A pharmaceutical composition should be a clear solution and if it is present as a lyophilisate it should also lead to a clear particle-free solution when reconstituted which is also free of soluble protein aggregates.
Numerous processes and additives are known for the stabilization of proteins in solutions. For example the stabilization of proteins by adding heat-shock proteins such as HSP25 is for example described in EP-A 0 599 344. The stabilization of antibodies by adding block polymers composed of polyoxy-propylene and polyoxy-ethylene and by phospholipids is described in EP-A 0 318 081. EP-A 0 025 275 describes the stabilization of immunoglobulin by adding a salt of a basic substance containing nitrogen such as arginine, guanidine or imidazole. Other suitable additives for stabilization are polyethers (EP-A 0 018 609), glycerin, albumin and dextran sulfate (U.S. Pat. No. 4,808,705), detergents such as Tween.RTM.20 (DE 26 52 636, GB 8514349), chaperones such as GroEL (Mendoza, J. A. Biotechnol. Tech. 10 (1991) 535-540), citrate buffer (WO 93/22335) or chelating agents (WO 91/15509). Although these additives enable proteins to be stabilized to a certain extent in aqueous solutions. It has, however, turned out that none of the processes known in the prior art is suitable for stabilizing proteins during repeated freezing and thawing processes in such a way that no soluble or insoluble aggregates or only negligible amounts for therapeutic purposes are formed during rethawing, during storage at temperatures below 0.degree. C. or when a solution is reconstituted after lyophilization.
In EP-A 0 314 095 a lyophilisate of a plasma protein such as factor VIII is described which contains histidine buffer as a buffer substance and calcium chloride as an additive and is present in a high ionic strength (0.35 to 1.2 mol/l NaCl).
A lyophilisate of a plasma protein such as factor VIII is described in EP-A 0 315 968 which contains 0.5 to 15 mmol/l sodium chloride or potassium chloride, 0.01 to 10 mmol/l lysine hydrochloride and 0.2 to 5 mmol/l histidine as a buffer ion. However, histidine buffer is not suitable for stabilizing proteins and for preventing aggregate and particle formation when lyophilisates of proteins are reconstituted.